Energy harvesting: challenges for wireless monitoring applications

Energy harvesters deserve the attention they're receiving, the advent of what can be made possible through the use of ambient energy to power devices has intrigued a wide variety of technologists, developers and adopters.

IDTechEx follows developments worldwide and helps recognize potential hurdles, challenges and requirements that will increase adoption of energy harvesting and lead to further penetration of sustainable energy technologies.

Although TRW is mainly involved with components and systems for the automotive industry, the company's involvement in the energy harvesting space takes a step back and doesn't limit itself to vehicle applications for harvesters. Therefore, roadside infrastructure sensors are researched at TRW, aimed at monitoring traffic, potential accident hazards, accidents and its effects on roads, etc. The Swiss branch of TRW is also researching and developing its own thermoelectric generator.

It is interesting to point out that TRW is one of the world's leading suppliers of tyre pressure monitoring systems (TPMS) but instead of using energy harvesters for those (which could cost several tens of Euros), 60 cent batteries are utilized and perform adequately. According to Dr Hazelden, cost is a major driver in applications such as TPMS where the use of batteries is not regulated; a low cost coin cell will always be preferred over an expensive energy harvester. Energy harvesters would make a lot more sense in applications where there are restrictions on the use of batteries (e.g. aerospace), in which case they would be part of the necessary enabling technologies that would make wireless sensing/monitoring a reality.

Structural monitoring
At an energy harvesting workshop on the 4 May, Kenichi Soga, professor of civil engineering from the University of Cambridge gave insight on the use of monitoring for structures that were built in the past with a "let's build them and see how long they last..." approach. Several of these structures are by now a few decades old and pose potential risks if their integrity is compromised over time. A very interesting example of use of integrity sensors in a project was during some work undertaken for the London Underground, making sure that tunnel tiles did not shift or move, leading to width changes that could be detrimental to passing trains or even fears of collapse. Again, interestingly, batteries were used for these sensors, provided by Tadiran technology. At a cost of about £40 for the battery and £200 for the whole sensor, batteries were considered, the best, most reliable option, with a lifetime of approximately 2 years, and the sensor taking measurements at a rate of 1 measurement/minute.

Identified challenges
High costs for energy harvesters, reliability of new technologies when compared with established ones, advances in existing competing technologies (such as batteries and supercapacitors) as well as convincing potential customers of the advantages offered by new technologies as well as identifying the correct harvesting solution for the correct application tend to be recurrent challenges for the energy harvesting sensor.

It is not always easy to compete on the merits and added benefits of new devices, especially when an additional cost accompanies them. Initial costs of ownership and infrastructure necessary can add to the scepticism towards adopting innovative solutions. What tends to be important in efforts to alleviate scepticism is the use of proven solutions as examples that can convince of the real value behind the initial installation expenses. EnOcean's implementations are a great example of this and that can be seen from the large numbers of customers that have adopted the company's solutions (over 160,000 buildings are currently using EnOcean products, from wireless light switches to occupancy sensors and sensor networks for both building and industrial facilities). Such successful implementations raise the profile of energy harvesting technologies and increase awareness of potential users and the interest in finding elegant solutions to problems that cannot be solved without energy harvesting.

For information on this event or to apply for a press pass, please contact Cara Harrington.